ML20138H156

Safety Evaluation Accepting Licensee 850313 Decision to Discontinue Annual Radiographic Exam of 3-inch Loop a Charging Line Thermal Sleeves & Restricted Use of Normal Charging Line

ML20138H156
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	10/18/1985
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20138H152	List: ML20138H149 ML20138H156
References
TAC-48518, TAC-57258, NUDOCS 8510280290
Download: ML20138H156 (3)

Text

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! E ko NUCLEAR REGULATORY COMMISSION UNITED STATES h  : WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i

RADIOGRAPHIC EXAMINATION OF CHARGING LINE THERMAL SLEEV'ES TROJAN NUCLEAR PLANT

{ PORTLAND GENERAL ELECTRIC COMPANY '

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DOCKET NO. 50-344 I. INTRODUCTION During the 1982 refueling outage at the Trojan Nuclear Plant (the i facility), the lower reactor vessel area and internals were inspected

, while all fuel assemblies were removed from the vessel. This inspection revealed the presence of several loose objects beneath the lower core plate. Upon removal and examination, it was detennined the loose objects were whole and partial thennal sleeves which appeared to have come from j the 10-inch safety injection-to-RCS (Reactor Coolant System) cold leg i piping nozzles. Ultrasonic examination of these piping nozzles indicated j that all four 10-inch thermal sleeves were missing.

Based on these findings, radiographs were taken of the 3-inch,10-inch j and 14-inch nozzles in each reactor coolant loop utilizing thermal i

sleeves. These radiographs confirmed the 10-inch nozzles were missing i and indicated one of the two attachment welds for the 14-inch pressurizer l surge line nozzle thermal sleeve was broken. Radiograpl.s of the 3-inch l

charging line nozzles showed both thennal sleeves to be in place.

Attachment welds for the charging line thermal sleeve in Loop D appeared to have experienced no degradation since the original construction

examination was perfonned. In the Loop A nozzle, however, the attachment l weld appeared to have a small crack, approximately one-eight inch long, j which was not visible in the original radiograph.

By letter dated July 9,1982, the Portland General Electric Company (the licensee) transmitted a description of the above findings and a safety evaluation justifying operation in the "as-found" condition with the 10-inch thermal sleeves removed. Despite this evaluation, the licensee elected to remove the loose 14-inch thermal sleeve for economic reasons.

i Since the apparent small crack in the 3-inch thermal sleeve was found in l the normal charging line and not in the alternate charging line, the licensee comitted in the July 9,1982 letter to use the alternate

! charging line whenever possible in the future. In order to maintain

' surveillance of the remaining 3-inch thermal sleeves, the licensee also

, committed to radiograph the 3-inch thennal sleeves during annual i

refueling outages.

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l In response to a request from the staff, a more detailed safety evaluation prepared by the NSSS vendor (Westinghouse) was also submitted by the licensee by letter dated July 22, 1982. This submittal confimed the conclusions of the July 9, 1982 submittal. Based on the results of the staff's review of the licensee's submittals, the NRC, by letter dated August 12, 1982 from R. H. Engelken to B. D. Withers, advised the licensee that the staff had no objection to the resumption of facility i

operations for Cycle 5; and operations were subsequently resumed. The staff also advised the licensee that a detailed generic study of thermal sleeves was currently undemay and that if further action was needed, the licensee would be notified. No further requirements relating to this matter, however, were established and transmitted to the licensee.

By letter dated March 13, 1985, the licensee infomed the NRC the facility did not plan to continue the annual radiography of the 3-inch thermal sleeves and would discontinue the restriction on use of the normal charging line. The purpose of this Safety Evaluation, therefore, is to evaluate the effect an safety of this decision by the licensee.

II. EVALUATION Introduction. The licensee's letter of March 13, 1985 cites two bases for its decision to teminate annual radiography of the 3-inch thermal sleeves and whenever discontinue practicable. thebases These policy of using)the are: alternateincharging (1 the indication the Loopline A

thermal sleeve, which had been interpreted as a crack, is not growing and is now judged to be a non-relevant indication; and (2) the safety evaluation transmitted by the licensee's letter of July 9,1982, indicates operation with failed 3-inch thermal sleeves would not constitute an undue hazard to safety. Each of these is discussed below.

Radiographic Examination. As a result of the commitment by the licensee to radiograph the 3-inch thermal sleeves during annual refueling outages, the licensee states additional radiographs were obtained for both the 1983 and 1984 refueling outages. The licensee also states the 1982, 1983 and 1984 radiographs, along with the original 1974 radiograph, have been re-evaluated using computer digital enhancement. According to the ifcensee, this was done to determine whether the 1982 indication in the attachment weld of the Loop A thermal sleeve was a crack or a non-relevant indication. The licensee notes the indication was not visible in the original 1974 radiograph. The licensee also states, however, that evaluation using computer digital enhancement of the 1974, 1982,1983 and 1984 radiographs clearly shows the indication reported in 1982 is not a crack. Instead, the licensee considers the indication non-relevant and most probably caused by a weld geometry condition. In addition, the licensee states there is no evidence the indication is growing.

Safety Evaluations. Both of the licensee's safety evaluations (July 9 and 22, 1982) assume, contrary to expectations, the 3-inch thermal sleeves are dislocated from their respective piping nozzles and transported into the RCS loops. Having entered the RCS, the evaluations then consider the possible damage or other conditions that might be caused by intact l thermal sleeves or pieces thereof. The July 22, 1982 evaluation also l

,' addressed the effect of the absence of the thermal sleeves on nozzle l stresses. As noted above, the staff reviewed these evaluations in 1982 and concluded they had r.o objection to resumption of facility operation in Cycle 5. No additional requirements have been established by the staff since this earlier approval. .

Discussion. The licensee committed to the measures now planned to be discontinued, in the July 9,1982 letter, in response to the belief a small crack existed in the attachment weld of the 3-inch thermal sleeve located in the normal charging line nozzle. We note, however, the radiographs obtained since that time have failed to show any crack growth. In addition, interpretation of the 1974, 1982, 1983 and 1984 radiographs of this region, using computer digital enhancement, concludes the indication seen in the 1982 radiograoh was, in fact, not a crack but a non-relevant indication caused by a we!J geometry condition. It therefore appears there is little reason to believe either of the 3-inch thermal sleeves is likely to fail. Nonetheless, even if such failure should occur, the safety evaluations submitted by the licensee in 1982, and accepted by the staff, indicate such failure would not result in an undue safety hazard. This conclusion is also supported by the operating experience of the facility, which operated without incident while four 10-inch thermal sleeves became detached and were transported to the RCS.

Conclusion. Based on the foregoing we conclude the licensee's decision to discontinue annual radiographic examination of the 3-inch thermal sleeves and discontinue restricted use of the nornal charging line will not result in an undue risk to the health and safety of the public, and is therefore acceptable.

Principal Contributor:

G. Zwetzig, Region V Date: October 18, 1985 0

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